Wings on Cars

Don't let the air up there spoil the traction down here

Feature Article from Hemmings Motor News

The idea of applying aerodynamic principles to cars pre-dates the Wright Brothers' first flight by several years when Camille Jenatzy of Belgium set a land speed record by driving the electric Jamais Contente torpedo-shaped car to a speed just over 65 MPH. While the idea was a gallant try, Jenatzy's high perch in his seat had him practically sitting on top of the car and negated any effect at streamlining it may have accomplished.
While the space race in the 1950s left us with some very cool, rocket-inspired taillamps that did little to improve actual aerodynamics, it took until the 1960s before true, science-backed manipulation of the air made its way onto an automobile. Within a few years of the Chaparral 2E's debut in the 1966 Can-Am series, wings would appear at almost every level of racing, from NASCAR to Formula 1 to NHRA. They even made it to the showroom with the likes of the outrageous gigantic wings found on the 1969 Dodge Charger Daytona.
By then, aerospace engineers had mastered the wing. There are four forces that affect a wing's ability to produce flight: thrust, lift, drag and weight. The wing of an aircraft must create enough lift with a given amount of thrust to overcome drag and weight to keep an airframe aloft. It performs this gravity-defying feat by speeding up the air that passes over the curved side on top, which reduces pressure above, and slowing down the air on the flat side below, which increases pressure. That difference in pressure creates lift, something most desirable in an airplane.
When you flip that wing over, the result is negative lift, or downforce. At speed, a correctly mounted inverted wing will create positive pressure above and negative pressure below. If engineered correctly, this force pushes the car down, ultimately acting on the tires to give them greater capacity for grip, improving a car's ability to turn, brake and accelerate.
Unfortunately, while a well-designed wing will increase a car's downforce by several orders of magnitude of the weight of the wing, there is still a price to pay and that price is called drag, something that ground-bound and flying vehicles alike must fight. Drag is the resistance of an object moving through the air. Think about sticking your hand out the window at 65 MPH; it gets pushed back by the moving air. That's drag. The best wings provide downforce with a minimum of drag, but any object that is in the airflow adds at least some drag. A more aggressive wing may increase downforce, but it also increases drag.
Wings come in many different shapes and sizes, from the multiple types found in front and back of both Indy and Formula 1 cars, to wings seemingly 10 feet off the ground in an NHRA top fuel car. A spoiler is a different sort of animal. Unlike a wing, which benefits a car by taking advantage of the pressure change effected by the flow of air over and under it, a spoiler is used to, well, spoil the airflow. At the back of a sedan, the air moving down over the backlight and onto the trunk acts like that flowing over a wing and creates lift--good for an airplane, bad for a fast car. The spoiler breaks up that flow and puts more forward pressure on the air, resulting in less lift and potentially some downforce, but no air flows under it, as with a wing.

This article originally appeared in the June, 2012 issue of Hemmings Motor News.